This invention relates to a shift device for a hydraulic transmission and more particularly to an improved shifting arrangement for hydraulic transmissions that will insure that the transmission is locked in a neutral condition when the shift lever is placed in its neutral condition.
Hydrostatic transmissions are used for a wide variety of purposes and applications. Such transmissions include a fluid pump that is driven by an internal combustion engine and which supplies fluid under pressure to a fluid motor that drives a driven object. The speed at which the output object is driven depends upon the delivery of the fluid pump which is varied conventionally by some form of swash plate mechanism. Such transmissions frequently operate not only between a neutral and a forward drive condition but also between a neutral and a rearward drive condition. Most frequently, the swash plate is controlled by a control shaft that is mounted in the transmission housing and which is itself is rotated from a remotely positioned shift lever through an intermediate shift linkage assembly. Because of the incorporation of such linkage assemblies, it is sometimes difficult to insure that the transmission control shaft is placed in its neutral condition at the same time the shift lever is in its neutral condition. As the complexity of the linkage system increases, the difficulties to insure this coincidence of neutral conditions becomes more and more difficult.
It has, therefore, been proposed to employ a detent mechanism for locking the transmission control shaft in its neutral condition. However, the detent mechanisms previously proposed for this purpose are not completely satisfactory in that they do not necessarily insure that the transmission is in fact in its neutral condition when the shift lever is in its neutral condition.
It is, therefore, a principal object of this invention to provide an improved detent locking mechanism for a hydrostatic transmission that will insure that the transmission is in its neutral condition when the shift lever is in its neutral condition.
It is a further object of this invention to provide an improved and adjustable detent mechanism for a hydrostatic transmission that acts directly on the transmission control shaft so as to insure that the control shaft will be retained in its neutral condition.
In addition to the difficulties as aforedescribed, there is a further problem in connection with the prior art type of neutral detent mechanisms. These mechanisms, as has teen noted, are intended to bias the transmission control shaft to its neutral condition. However, because of the fact that the transmission control shaft is connected to the shift control lever, the detent mechanism must move the entire interconnecting linkage system and the shift lever when the control shaft is biased to its neutral condition. This requires greater than acceptable spring rates and also means that the operator must release the shift lever in order for the detent mechanism to operative.
It is, therefore, a still further object of this invention to provide an improved linkage assembly for a transmission control shaft embodying a neutral detent lock wherein the detent lock can lock the transmission without having to move the entire linkage assembly and shift control lever.